Patent GB-626966-A (GB)
Title: Improvements in and relating to radio aids to navigation
IPC: G01S1/24
Filed: 1946-08-26
Abstract: 626,966. Radio-navigation. UTTLEY, A. M. Aug. 26, 1946, No. 25446. [Class 40 (vii)] A navigational aid, for use with a hyperbolic navigational system comprising at least three spaced, fixed, transmitters, comprises means for deriving from signals received from said transmitters two currents or voltages dependant on the difference between, on the one hand, the time intervals between signals arriving from two pairs of transmitters respectively and, on the other hand, those between signals which would be received at a chosen point, and means fed with said currents and voltages to indicate the disposition of the craft in which the aid 'is carried relative to a course passing through or embracing the chosen point. The invention is applicable to hyperbolic radio-navigational aids of either pulse or continuous wave types. If A, Fig. 1, is the position of the craft, and D the chosen point defined by hyperbolic lattice lines Dx and Dy. Then, assuming curves Dx and Dy to have large radii of curvature as will be the case except close to the transmitters, if the course of the craft is such as to maintain the: distances x and y in a constant ratio the locus of A will be the dotted line through D. The time intervals corresponding to x and y may be obtained by presenting the four time intervals corresponding to the co-ordinates of A and D in the form of currents or voltages and by using simple computing means to derive the required two differences. Alternatively the computing means may be associated with strobing currents of such a kind that when strobes are moved from positions corresponding to D to lock with positions corresponding to A, currents or voltages corresponding to time intervals x and y are available directly. The derived time intervals x and y require to be multiplied by scale factors a and b, dependent on the contour spacing in the area concerned (these factors may be marked on the map) to determine the actual distances from the craft to the two lattice lines. If these distances ax and by are indicated continuously, a point Al between A and D can readily be identified. A two-phase D.C. meter may be used as a course indicator and arrangements to bring the needle to a vertical position for any ratio of x to y incorporated. If reference voltages proportional to x and y are fed to computing means which provide an output proportional to #x<2>+y<2> and this output is used to give an indication which is held constant, the craft will follow an eliptical orbit about D. It is generally preferred to use circular orbits, and Fig. 2 shows the factors involved where this type of orbit is required. With reference to rectangular axes Dx and the perpendicular through D, the hyperbolic difference co-ordinates of A, namely ax and by, become (a cosec #x+bcot#y) and by where # is the angle of intersection of the lattice lines Dx and Dy in the neighbourhood of D and the lattice lines are assumed to be straight in the area concerned. The range of A from D is given by : AD = (a cosec #x+-b cot #y) sin #+by cos # (1 # being the bearing angle of AD as shown. For a circular orbit, therefore, [(a cosec #x+b cot #y sin #+by cos #] must be independent of 6. The value of # may be represented by: Equations (1) and (2) may be re-written: AD sin #=(ax+b cos #y) sin #+(b sin #y) cos #...... (3) and (ax+b cos #y) cos # - (b sin #y) sin #=0 . . (4) An electro-mechanical computing device for solving these equations is described with reference to Fig. 3 (not shown). This computor fed with voltages representing the time differences x and y and being pre-set according to the values of the scale factors a and band the angle # gives an output proportional to the range AD and may also indicate the angle 6. To fly a circular orbit of given radius an opposing voltage proportional to the required range is fed to a centre zero meter together with the output of the computor to provide an indication of any deviation from a constant range AD. If the craft travels to maintain 0 constant it will move towards D along substantially a straight line.